1. Technical Field
This application discloses a light-emitting diode device, comprising a light-emitting layer not overlapped with the peak zone of the wave intensity distribution curve along the direction of the epitaxy growth.
2. Reference to Related Application
This application claims the right of priority based on TW application Ser. No. 097122631, filed Jun. 17, 2008, entitled “LIGHT-EMITTING DEVICE”, and the contents of which are incorporated herein by reference.
3. Description of the Related Art
The luminescence principle of the light-emitting diode (LED) devices is to generate light by the energy difference of the electron moving in the n-type semiconductor and the p-type semiconductor, which is different from that of the incandescent light, and it is the reason for the light-emitting diode device to be called as cold light sources. Besides, the LED devices have the characteristics of high durability, long operation life, small volume and low power consumption and so on so the LED is attractive in lighting market and is viewed as the new generation lighting device.
FIG. 1 shows a conventional light-emitting diode device 100 including a substrate 10, an epitaxial structure 12 formed on the substrate 10, and a least an electrode 14 formed on the epitaxial structure 12. The epitaxial structure 12 includes a first type semiconductor layer 120, a light-emitting layer 122, and a second type semiconductor layer 124 formed subsequently. Usually, the structure of the light-emitting layer 122 is a multi-quantum well structure.
FIG. 1B is schematic illustration of the bandgap distribution of the conventional light-emitting diode device 100. As shown in FIG. 1B, the structure of the light-emitting layer 122 of the light-emitting diode device 100 includes a plurality of quantum barrier layers 130 and a plurality of quantum well layers 132 inserted between the quantum barrier layers 130 wherein the bandgap of the material of the quantum well layers 132 is usually smaller than that of the quantum barrier layers 130. The quantum well layers 132 not only extracts light, but also absorbs the light that having the wavelength the same with or shorter than the light extracted form the quantum well layers 132 when the light passes the quantum well layers 132. The light absorption effect of the quantum well layers 132 described above exists in the light-emitting element of GaN or AlGaInP material system, especially in AlGaInP material system.
In addition, in order to increase the external efficiency of the light-emitting diode device 100, the quantum barrier layers 130 and quantum well layers 132 are repeatedly stacked in stagger with 20 to 100 layers, and the effect of the light extracted from the light-emitting layer 124 to be absorbed by the quantum well layers 132 is therefore aggravated as the quantity of the stacked layers and the thickness of the quantum well layers 132 increased.
FIG. 1C illustrates the intensity distribution curve of the conventional epitaxial stack structure 12 of the light-emitting diode device. As shown in FIG. 1C, the conventional light-emitting diode device 100 has a intensity distribution curve B along the epitaxy growth direction A, and has a peak zone in the intensity distribution curve B. The peak zone means a zone that has the intensity value higher than 90% of the max intensity value in the intensity distribution curve B (the zone formed by the dotted line B1, B2 and the intensity distribution curve B), wherein the peak zone is overlapped with the light-emitting layer 122. Besides, by calculating the percentage of the zone of the intensity distribution curve B overlapped with the light-emitting layer 122 (the slash zone) to the zone of the total intensity distribution curve B the optical confinement factor τactive layer of the light-emitting layer 122 can come out. As shown in FIG. 1C, the conventional τactive layer is about 60%. As described above, because most light extracted from the light-emitting layer is confined in the area of the light-emitting layer, and the material of the light-emitting layer is easy to absorb light makes it hard to raise the light efficiency of the light-emitting diode device 100.